Atrial Septal Defect, Ostium Primum
- Author: Shannon M Rivenes, MD; Chief Editor: Steven R Neish, MD, SM more...
Background
An ostium primum atrial septal defect (ASD), as seen in the image below, is located in the most anterior and inferior aspect of the atrial septum. It is the simplest form of atrioventricular (AV) canal or AV septal defect. These defects are often associated with trisomy 21.
Gross pathology specimen viewed from the opened left atrium and left ventricle, demonstrating a partial atrioventricular (AV) canal defect. An ostium primum atrial septal defect (ASD) marked by an asterisk (*) is visualized in the inferior aspect of the interatrial septum. An ostium secundum ASD marked by 2 asterisks (**) is also noted. The mitral valve is cleft and the leaflets are thickened and rolled, suggestive of chronic mitral regurgitation. LA = Left atrium; LV = Left ventricle; MV = Mitral valve. During fetal development, the rudimentary atrium is divided by the septum primum, except for an anterior and inferior space that is the ostium primum. The ostium primum is sealed by fusion of the superior and inferior endocardial cushions around 5 weeks' gestation. Failure to do so results in an ostium primum ASD. The endocardial cushions also contribute to the complete formation of 2 separate AV valves and the inlet interventricular septum. For this reason, ostium primum ASDs commonly are associated with malformations of these structures.
Ostium primum ASDs may occur in isolation but most commonly present with a cleft in the anterior leaflet of the mitral valve. This is sometimes termed a partial AV canal defect or a partial AV septal defect. In this case, a 5-leaflet AV valve is arranged so that separate right and left components (a tricuspid valve and a mitral valve) are present. The leaflets connect to each other and then adhere to the crest of the interventricular septum. This results in obligatory shunting at the atrial level with no ventricular level shunting. Generally, a commissure is observed between the left superior and inferior bridging leaflets because of abnormal fusion of the left tubercle of the superior and inferior cushions, which results in a cleft in the anterior leaflet of the mitral valve.
Pathophysiology
Shunting is predominantly left-to-right in the absence of pulmonary vascular disease or significant right ventricular outflow tract obstruction. This results in volume overload of the right atrium and ventricle and pulmonary overcirculation. If the mitral valve cleft causes significant mitral regurgitation, the left side of the heart also becomes volume overloaded. A left ventricle to right atrium shunt can be present, which further overloads both the right and left heart.
Epidemiology
Frequency
United States
Ostium primum ASDs are most commonly associated with Down syndrome (trisomy 21). The incidence of trisomy 21 is 1 per 800 live births, with an increased prevalence noted in children born to older mothers.
- The overall risk of congenital heart disease in patients with Down syndrome is 40-50%. Approximately 65% of those affected have some form of AV septal defect.
- The inherited risk for children of parents who have an AV septal defect is reported as 9-14%.
Mortality/Morbidity
The presence and degree of associated mitral regurgitation and/or left ventricle to right atrium shunting generally determine symptoms.
Those with either no cleft or a cleft with a mild degree of mitral regurgitation are often asymptomatic. Patients typically are referred for evaluation of a heart murmur in childhood and generally survive well into adulthood. However, adults who have not had the condition repaired often become symptomatic from congestive heart failure (CHF) by age 45 years. Rarely, patients are reported to present in the seventh decade of life. Dyspnea on exertion and fatigue are usual adult complaints. Palpitations secondary to atrial fibrillation or flutter also are common.
Those with more severe mitral regurgitation or left ventricle to right atrium shunting often present in the first 2 years of life. Mortality has been reported to be as high as 30% in this subpopulation in the first year of life.
Although relatively rare, pulmonary vascular obstructive disease may occur in patients with long-standing substantial shunts and significant mitral regurgitation.
Children with trisomy 21 are at higher risk than the general population of developing pulmonary vascular obstructive disease at a younger age. Potential reasons for this include chronic upper airway disease, tonsillar and adenoid hypertrophy, and inadequate alveolarization of the terminal bronchioles, leading to a decreased surface area of the vascular bed.
Sex
The male-to-female ratio is 1:1.
Age
Patients with smaller defects and little or no mitral regurgitation may present at any age with a murmur and/or an abnormal ECG. Those with more severe mitral regurgitation typically present with CHF in the first 1-2 years of life.
Murashita T, Kubota T, Oba J, et al. Left atrioventricular valve regurgitation after repair of incomplete atrioventricular septal defect. Ann Thorac Surg. Jun 2004;77(6):2157-62. [Medline].
Morris CD, Reller MD, Menashe VD. Thirty-year incidence of infective endocarditis after surgery for congenital heart defect. JAMA. Feb 25 1998;279(8):599-603. [Medline].
Najm HK, Williams WG, Chuaratanaphong S, et al. Primum atrial septal defect in children: early results, risk factors, and freedom from reoperation. Ann Thorac Surg. Sep 1998;66(3):829-35. [Medline].
Michielon G, Stellin G, Rizzoli G, Milanesi O, Rubino M, Moreolo GS, et al. Left atrioventricular valve incompetence after repair of common atrioventricular canal defects. Ann Thorac Surg. Dec 1995;60(6 Suppl):S604-9. [Medline].
Bergin ML, Warnes CA, Tajik AJ, Danielson GK. Partial atrioventricular canal defect: long-term follow-up after initial repair in patients > or = 40 years old. J Am Coll Cardiol. Apr 1995;25(5):1189-94. [Medline].
Agny M, Cobanoglu A. Repair of Partial Atrioventricular Septal Defect in Children Less than Five Years of Age: Late Results. Ann Thorac Surg. May 1999;67(5):1412-4. [Medline].
Arky, Ronald. Physicians' Desk Reference. 52nd ed. Montvale, NJ: Medical Economics Co Inc; 1998:784-7, 1051-1062, 1219-1221.
Castaneda AR, Jonas RA, Mayer JE. Atrioventricular canal defect. In: Cardiac Surgery of the Neonate and Infant. 1994:167-86.
Cheitlin MD, Douglas PS, Parmley WW. 26th Bethesda conference: recommendations for determining eligibility for competition in athletes with cardiovascular abnormalities. Task Force 2: acquired valvular heart disease. J Am Coll Cardiol. Oct 1994;24(4):874-80. [Medline].
Del Nido PJ, Bichell DP. Minimal-access surgery for congenital heart defects. Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 1998;1():75-80. [Medline].
Garson A Jr, Bricker JT, Fisher DJ. The Science and Practice of Pediatric Cardiology. 2nd ed. Williams & Wilkins; 1998:1158-179.
Giamberti A, Mazzera E, Di Chiara L, Ferretti E, Pasquini L, Di Donato RM. Right submammary minithoracotomy for repair of congenital heart defects. Eur J Cardiothorac Surg. Dec 2000;18(6):678-82. [Medline].
Gilman AG, Goodman LS, Nies AS. Goodman and Gilman's The Pharmacological Basis of Therapeutics. 8th ed. 1990:721-5, 749-63, 814-839.
Graham TP Jr, Bricker JT, James FW, Strong WB. 26th Bethesda conference: recommendations for determining eligibility for competition in athletes with cardiovascular abnormalities. Task Force 1: congenital heart disease. J Am Coll Cardiol. Oct 1994;24(4):867-73. [Medline].
Kaur A, Srivastava S, Lytrivi ID, Nguyen K, Lai WW, Parness IA. Echocardiographic evaluation and surgical implications of common atrioventricular canal defects with absent or diminutive ostium primum defect. Am J Cardiol. Jun 1 2008;101(11):1648-51. [Medline].
Lange A, Mankad P, Walayat M, et al. Transthoracic three-dimensional echocardiography in the preoperative assessment of atrioventricular septal defect morphology. Am J Cardiol. Mar 1 2000;85(5):630-5. [Medline].
Marino B, Digilio MC, Toscano A, et al. Congenital heart diseases in children with Noonan syndrome: An expanded cardiac spectrum with high prevalence of atrioventricular canal. J Pediatr. Dec 1999;135(6):703-6. [Medline].
Perloff JK. The Clinical Recognition of Congenital Heart Disease. 4th ed. WB Saunders; 1994:349-80.
Pretre R, Dave H, Kadner A, Bettex D, Turina MI. Direct closure of the septum primum in atrioventricular canal defects. J Thorac Cardiovasc Surg. Jun 2004;127(6):1678-81. [Medline].
Sadler TW. Langman's Medical Embryology. 5th ed. Baltimore, MD: Williams & Wilkins; 1985:176-84.
Snider AR, Serwer GA, Ritter SB. Echocardiography in Pediatric Heart Disease. 2nd ed. Harcourt Health Sciences Group; 1997:277-89.
Zanchetta M, Rigatelli G, Pedon L, et al. Role of intracardiac echocardiography in atrial septal abnormalities. J Interv Cardiol. Feb 2003;16(1):63-77. [Medline].
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